Crystallization behavior and physical properties of linear 2-arm and branched 4-arm poly(l-lactide)s: Effects of branching

The pure effects of branching architecture on crystallization and thermal properties were investigated using linear 2-arm and branched 4-arm poly(l-lactide) (2L and 4L, respectively) polymers having a wide range of number-average molecular weight (Mn) values of 5.0 × 103–6.0 × 104 g mol−1. 2L and 4L were synthesized by bulk ring-opening polymerization of l-lactide initiated with tin(II) 2-ethylhexanoate (i.e., stannous octoate) in the presence of bifunctional coinitiator of 1,3-propanediol and tetrafunctional coinitiator of pentaerythritol with the identical carbon numbers between the hydroxyl groups. Branching architecture of 4L delayed or disturbed non-isothermal crystallization during heating and isothermal crystallization, compared to those of linear architecture of 2L. In contrast, the glass transition temperature or segmental mobility, melting temperature or crystalline thickness, transition crystallization temperatures of crystalline form, and crystal growth mechanism were not affected by the presence of branching, but depended on Mn or Mn per one arm.